Field
Embodiments described herein generally relate to antennas capable of communication and navigation using multiple frequency bands.
Background
Satellite communication and navigation systems can be used to provide a broad set of services, e.g., Global Navigation Satellite System (GNSS), which includes Global Positioning System (GPS). To be able to transmit or receive from satellites, handsets used in these systems often use circularly polarized antennas because circularly polarized radiation is generally insensitive to ionospheric polarization rotation. Moreover, these antennas preferably are also able to provide gain from zenith down to near the horizon to allow for communications with low elevation angle satellites.
Helical antennas are one example of a type of antennas that are often used for handsets in satellite communication or navigation systems. For example, a quadrifilar helical antenna (QHA) can be used to provide right-handed circularly polarized (RCHP) gain at angles from zenith down to the horizon. Further enhancing their appeal, QHAs are generally small, light-weight, and cheap to fabricate.
A QHA includes four arms wrapped around a cylindrical surface, for example the surface of a dielectric rod. Each of the arms can be formed out of a copper trace and each can be separately fed at the base of the antenna. To enhance its bandwidth, a QHA can be provided with four pairs of arms (termed a “folded QHA”). In each pair, one arm (termed the “driven arm”) is connected to a feed point which is connected to the circuit and electronics which sends and/or receives signals to or from the antenna. The other arm, termed the (“folded arm”), provides an extension of the driven arm and/or a return path for the current.
Although conventional QHAs provide RHCP gain over a wide range of angles, their frequency bandwidth is often limited. For example, many conventional QHAs only can operate at one or two GNSS frequency bands. This is not sufficient for many new GNSS systems which use additional GNSS bands. Moreover, some communication systems use different frequency bands at which conventional GNSS QHAs are not operational, e.g., the frequency bands used for Iridium and for UHF communications.